Various methods of spinal immobilization have been known and used for many years to correct spinal irregularities, instability and displacement, in order to restore stability to traumatized areas of the spine. The preferred treatment for spinal stabilization is immobilization of the joint by surgical fusion, or arthrodesis. Spinal fixation is used, for example, to treat vertebral displacement and management such as kyphosis, spondylolisthesis and rotation; segmental instability, such as disc degeneration and fracture caused by disease, trauma, congenital defects, and tumors. It is found that immediate immobilization allows a bony union to form.
Spinal implant systems often include spinal instrumentation having connective structures such as round spinal rods which are placed on opposite sides of the portion of the spinal column intended to be immobilized. Fasteners such as screws and hooks are commonly utilized to facilitate segmental attachment of such connective structures to the posterior surfaces of the spinal laminae, through the pedicles, and into the vertebral bodies. These components provide the necessary stability both in tension and compression to achieve immobilization.
A concern of spinal fixation is where to secure the fixation device in the spine without damaging the spinal cord. The pedicles are usually chosen because they are strong enough to hold the fixation device even in patients with osteoporosis. Recently, posterior methods of fixation have been developed which use wires that extend through the spinal canal and hold a spinal rod against the lamina (such as the Luque system) or that utilize pedicle screws which extend into the pedicle and secure a plate which extends across several vertebral segments (such as the Steffee plate). A complete discussion of the various fixation systems are found in L. Wiltse, “Internal Fixation of the Lumbar Spine,” Clinical Orthopaedics and Related Research, 203: 2-219 (February 1986). Known implant configurations include facet screws, double distraction systems, compression distraction systems, springs, spinous process plates, wired implants and transpedicular screw and plate systems. Examples of spinal fixation systems are described in, U.S. Pat. No. 5,443,467 (Biedernann et al); U.S. Pat. No. 5,474,555 (Puno et al); U.S. Pat. No. 5,752,957 (Ralph et al); U.S. Pat. Nos. 5,733,286 and 5,817,094 (both of Errico et al); U.S. Pat. No. 5,863,293 and 2003/0199873 (both of Richelsoph); U.S. Pat. No. 5,882,350 (Ralph et al); U.S. Pat. Nos. 5,885,286 and 6,454,773 (both of Sherman et al); U.S. Pat. Nos. 5,910,142 and 6,113,601 (both of Tatar); U.S. Pat. No. 6,488,681 (Martin et al); U.S. Pat. No. 6,485,494 (Haider); U.S. Pat. No. 6,520,963 (McKinley); U.S. Pat. No. 6,554,834 (Crozet et al); and U.S. Patent Application Pub. Nos. 2002/0120272 and 2003/0125742 (both of Yuan et al); 2004/0102781 (Jeon); 2004/0158247 (Sitiso et al); 2004/0236330 (Purcell et al); 2005/0038430 (McKinley); and 2005/0049588 (Jackson). U.S. Pat. No. 5,474,555 presents figures showing in detail how its spinal implant system is implanted in vivo. The commercially available spinal fixation systems (such as those from DePuy Orthopaedics, Inc., Interpore Cross International, and U&I Corporation) and some of those described in the foregoing patents and applications, have a generally U-shaped body into which a pedicle screw is inserted, either from the top or the bottom of the U-shaped body. A spinal rod is secured in the spinal rod passageway of the U-shaped body by various means.
Pedicle screws allow spine surgeons to attach spinal rods or plates to the thoracic and lumbar spine. This rigidly immobilizes the spine segments, promoting a bone graft to grow into a fusion, welding spinal segments into one solid unit, reducing pain and stabilizing deformity without requiring complete immobilization of the patient for the extended period of time during the healing process. For example, a spinal fixation system may be installed in patients who are receiving fusion by autogenous bone grafts and later removed after the grafts are successful.
While many different pedicle screws have been developed, presently most pedicle screws are fixed axis devices which must be carefully aligned during insertion and fixation in the spine. Specifically, the screws must be drilled or screwed into the bone at a very specific angle to assure that the alignment hardware is exactly positioned such that the receiving portions of the fixation hardware are aligned so that the spinal rod can be passed there through without distorting the screw or putting an undesirable level of stress on the attachment point. As a result, the alignment procedure requires a considerable amount of time, increasing the possibilities of complications during surgery and, in many cases the alignment fails and must be repeated. Further, the insertion of the screw is dependent on the angle of alignment required, resulting in insertions that are not in the most secure or safe positions with respect to the vertebral bodies.
The art contains a variety of pedicle screw fasteners which permit a level of freedom with respect to the alignment of the screw and the coupling element. However, these teachings have generally been complex, and inadequately reliable with respect to durability. The considerable drawbacks associated with the prior art systems include limited angular adjustability, complexity, difficulty of properly positioning the coupling elements and the spinal rod, tedious manipulation of the many parts associated with the complex devices and the considerable cost associated with manufacturing such complex mechanisms. Accordingly, a need exists for an inexpensive, durable and simple vertebral alignment assembly that allows a surgeon to freely manipulate the alignment of the coupling hardware such that the spinal rods can be properly positioned with respect to the pedicle screw and vertebral bodies without a time consuming and potentially dangerous alignment procedure. Also, it is known that threaded fasteners can become loosened under the influence of cyclically applied loads commonly encountered by the spinal column. Furthermore, during assembly, excessive torque applied to a threaded fastener can cause damage to the fastener as well as to the connective device with which it is associated. Therefore, a need exists for a more reliable and effective mechanism for facilitating the attachment of screws, hooks and clamps to the connective structures of a spinal stabilization system, while providing the surgeon a means to easily align the spinal rod with the pedicle screw assemblies, and allowing the surgeon to ensure that the spinal rod is aligned when implanting the pedicle screw assemblies, and allowing the spinal rod to stay aligned in relation to the pedicle screw assemblies in vivo.